The present invention relates to a cap nut fluid coupling characterized by a high degree of sealability and ease of fitting the coupling to associated piping.
The rapid advance of high technology in recent years has made it necessary, as seen in the case of VLSI or super VLSI, to manufacture extremely large scale integrated circuits. In the manufacture of such an extremely large scale integrated circuit, a highly toxic fluid gas such as gallium arsenide (GaAs), a semi-conductor compound, is employed and a high-purity film is formed under extremely high vacuum conditions. For these reasons, it is obvious that the semi-conductor manufacturing equipment must possess a high degree of sealability.
All the flow-path elements for such equipment generally cannot be interconnected by welding, at lease some have to be interconnected mechanically. As a consequence, a fluid coupling with excellent mechanical sealability is an indispensible element for such equipment. For this purpose, there are a wide variety of fluid couplings available. A typical fluid coupling, as is illustrated in FIG. 1, consists of two sleeves 1 and 2 connected by means of a gasket 3, the connection being effected by screwing an externally threaded gland 4 carried by sleeve 1 into a cap nut 5 carried by sleeve 2. Such a connection using a cap nut, a connection which is quite simple and does not require a large amount of space, is primarily used for connecting pipes of small diameter. This means of connection, however, has several drawbacks. For example, when the cap nut is tightened, a torque due to friction between the cap nut 5 and the sleeve 2 acts on the sleeve and, as a consequence, the piping welded to the sleeve is twisted. Another drawback is that a rotation of the sleeve causes scratches on the surface of the gasket 3 which may result in leakage of fluid. To eliminate these drawbacks, it is common practice to provide chamfers 6 of two sides of the sleeve 2 by pressing a spanner against the chamfered sides. This task of tightening the cap nut 5, however, cannot be accomplished by a single worker since the worker must rotate the cap nut while at the same time immovably holding both the gland 4 and the sleeve 2. In addition, the task must be done with great care which makes assembly of the fluid coupling very inefficient.
Another conventional joint for preventing integral rotation fixedly interposes a ball 8 and a nut 9 between a sleeve and 7 and a screwed locking ring 10 by placing the ball 8 on the sleeve 7, covering the nut 9 thereon, engaging and welding the ring 10 to the sleeve 7. Such a joint is shown in FIG. 2 and is disclosed in G.B. Patent No. 518,930.
Since this conventional joint has a number of parts in a complicated structure and also has the problem of thermal influence during welding, the joint has the drawbacks that the assembly is very complicated and the joint cannot be simply used as an independent part. Thus, the joint has the disadvantages that it is inconvenient in the actual use and its available range is quite limited.